1. Technical Field
This invention relates generally to wireless ECG bio-potential measurement devices for measuring electrical bio-potential signals generated by the heart. More particularly, it relates to a new and improved leadless wireless ECG measurement system and method for measuring of bio-potential electrical activity of the heart that uses measurements obtained across a much smaller separation distance between electrode contact points, but yet retains the presentation of ECG waveforms which corresponds closely to existing ECG measurement standards, thereby preserving the waveform morphology, amplitude, and frequency components.
2. Prior Art
As is generally known in the art, an electrocardiograph is widely used by the medical profession in order to obtain an ECG (electrocardiogram) which is a measurement of bio-potential electrical activity of the heart from the surface of the skin. The conventional 12-lead electrocardiograph typically requires at least 10 wires to be attached via electrodes to the body of the patient at one end and to the electrocardiograph at the other end so as to measure the bio-potentials representing heart-signals and to transfer them via bipolar and unipolar leads into a 12-lead electrocardiogram.
ECG measurements have been conducted for over 200 years, and a standard configuration of the measurement vector leads have been adopted by the medical and engineering communities. This standard of leads formation and configuration require substantial separation of points of measurements on the surface of the skin, which necessitates connection of two remote points by lead wires into an instrumentation amplifier. This large separation between electrode contact points maximizes the surface area of the skin between the measurement electrode points and therefore maximizes the impedance, and measured voltage potential across the contact electrodes.
In early years, this was necessary for measurement of ECG due to lack of electronics that satisfy the measurement quality, signal-to-noise ratio, and cost constraints. Today, however, current electronics resolution, noise rejection, and amplification strength allows for ECG measurements across a much smaller separation distance between the contacting electrodes. ECG measurement standards, however, have been largely set and adopted with the original configuration of contact points preserving large separation distances between contacting electrodes.
The instrumentation amplifier is ideally used for the measurement of the ECG. The instrumentation amplifier typically rejects common mode noise using a common reference electrode to its two bipolar inputs, and amplifies the difference in potential between the two measurement electrodes as the measured bio-potential value. This bio-potential changes dynamically with the cardiac contraction and dilation due to depolarization and re-polarization of the cardiac muscle. The electric activity emanates from the Sinoatrial node (SA node) and spreads through the Purkinji fibers from the atrial upper portion to the ventricular portion of the cardiac muscle.
The electric activity surfaces from the cardiac muscle to the skin and dissipates throughout the conductive skin layer. Since the skin has electric impedances, the conductivity of the electric current varies depending on the direction of the measurement and the separation distance of between the measurement electrodes. The skin impedance varies dynamically depending on multiple factors, including the hydration status of the skin, blood flow vasodilators or vasoconstrictors, medications, cardiac output to name a few.
It will be noted that the 12-lead ECG provides spatial information about the heart's electrical activity in 3 approximately orthogonal directions. The orthogonal directions are namely (1) Right to Left, (2) Superior to Inferior, and (3) Anterior to Posterior. Thus, the standard ECG measurement involves the attachment of six electrodes to the chest or precordial area of the patient to obtain recordings of leads V1 through V6 and the attachment of four electrodes to the arms and legs in order to obtain recordings of leads I, II, III, AVR, AVL, and AVF. Subsequent to the attachment of the ten electrodes to the patient, there is then required the connecting of ten specific wires between each particular electrocardiograph terminal and the related electrodes of predetermined position.
In U.S. Pat. Nos. 6,441,747 to Khair et al. and 6,496,705 to Ng et al., there are disclosed a wireless, programmable system for bio-potential signal acquisition which includes a base unit and a plurality of individual wireless, remotely programmable transceivers connected to patch electrodes. The base unit manages the transceivers by issuing registration, configuration, data acquisition, and transmission commands using wireless techniques. The bio-potential signals from the wireless transceivers are demultiplexed and supplied via a standard interface to a conventional ECG monitor for display.
Further, there is shown in U.S. Pat. No. 7,403,808 to Istvan et al. a cardiac monitoring system for detecting electrical signals from a patient's heart and wirelessly transmit the signals digitally to a remote base station via telemetry. The base station converts the digital signals to analog signals which can be read by an ECG monitor.
In U.S. Pat. No. 5,862,803 to Besson et al., there is described a wireless medical diagnosis and monitoring equipment which includes an evaluation station and a plurality of electrodes which are arranged on a patient. Each of the plurality of electrodes includes elementary sensors, sensor control, transceivers, and transmission control units which are integrated in one single semiconductor chip.
In U.S. Pat. No. 4,981,141 to Jacob Segalowitz, there is disclosed an electrocardiographic monitoring system in which the heart-signal sensing electrodes are each coupled to the heart-signal monitor/recorder by respective wireless transmitters and corresponding respective receiving wireless receivers in a base unit.
One of the disadvantages encountered in the operation of the conventional ECG devices is that they utilize a large separation between the electrode contact points which requires maximum surface area of the skin and thus maximizes impedance and measured voltage potential across the contact electrodes. Another disadvantage suffered by the prior art ECG devices is that the numerous lengthy terminal wires coupled to the electrodes will frequently obstruct the patient and limit the freedom of movement of the patient. Further, the terminal wires often become intertangled with one another during their use, thereby rendering them difficult and cumbersome for the physician and/or technician. In addition, the conventional ECG devices and their attaching electrodes suffer from the problem of having a relatively large footprint.
Therefore, it would be desirable to provide a leadless wireless ECG measurement system and method for measuring of bio-potential electrical activity of the heart which operates on a more efficient and effective basis. Further, it would be expedient that the ECG measurement system overcomes all of the afore-mentioned shortcomings of the prior art discussed in connection with the application of the conventional electro-cardiographs used to obtain the electrocardiogram. The present invention represents a significant improvement over the aforementioned prior art U.S. Pat. Nos. 6,441,747; 6,696,705; 7,403,808; 5,862,803; and 4,981,141 which are hereby incorporated by reference in their entirety.